This invention is in the field of data processing circuitry, and particularly circuitry for interfacing between a number of terminals which communicate in a serial data format and a data processing system which operates upon parallel data. The invention has particular application in the telephone communications arts for handling the digital data portion of the interfacing between a plurality of call-answering terminals and a microprocessor based automatic call distribution section of a telephone switching system.
Heretofore, in data processing systems, conversion between serial and parallel data has been performed by appropriate transformation circuitry associated with each terminal in the system. With a central parallel data processing system and a plurality of remote terminals, for example, the data is communicated between the terminals and the central system over serial data lines. A pair of devices known as receiver-transmitters is associated with each terminal line running to the central processing system. One receiver-transmitter at the terminal converts parallel data to serial data for transmission over the serial data line, and it also converts incoming serial data to parallel data for use at the terminal. The second receiver-transmitter of the pair is connected to the central processing system for similar conversion between the serial data of the serial data line for the terminal and parallel data for use by the central system.
It can be seen that for a large number of terminals, a doubly large number of receiver-transmitters is necessary to communicate with the central processing system. It is also necessary to distribute the parallel date from the central system among the receiver-transmitters, and to assemble this serial data received from the terminals for transmission over the parallel data channel to the central system, which is accomplished by control circuitry.